In the manufacturing industries, especially in automobile manufacturing, the assembly and processing operations are currently performed with a high degree of automation including many types of robotic devices. Typically, a component part of the product being manufactured or a sub-assembly thereof is moved by a conveyor from station-to-station for a particular processing operation at each sequential station. In many factory installations, it is necessary to have a conveyor system which comprises two or more individual conveyors which must operate in timed relationship with regard to delivery or transfer of a workpiece. In such an installation, the two or more conveyors may have the single intersection or connection of their pathways, for transfer or the like, and one or more of the conveyors may extend over a very long distance within the factory. In automobile manufacturing, for example, the body shell of a car is moved by a main conveyor along a processing or assembly line which has a section provided with body painting stations. The body shell may be moved by the main conveyor through the painting section and continue to other sections of the conveyor and subsequent work stations along the same main conveyor. However, an inspection station prior to the painting section may detect a defect in the body shell which should be corrected before painting and a transfer station is provided to transfer the defective body shell to a secondary or feeder conveyor which will carry the body shell to a repair facility. Also certain of the body shells on the main conveyor may be programmed for two-tone painting and at a station following paint application on the main conveyor it is transferred to a separate feeder conveyor which carries it through other painting stations. A conveyor system of the type described requires a control system for controlling the movements of the carrier and other components of an individual conveyor in the system. For example, the movement of one conveyor must be started in timed relation with the starting or stopping of another conveyor in the same system or an actuator on one of the conveyors must be operated in timed relation with the movement of the other conveyor. Such coordinated or synchronized control and movement of individual conveyors is provided by the electrical control system.
It has been the common practice in the manufacturing industry to provide control for a conveyor system having plural individual conveyors by a master control system at a centralized single electrical control panel.
A typical prior art control system is costly and time consuming to install in the factory, especially for a conveyor system extending over a large distance. Such systems may include several individual conveyors and, in the prior art, utilize a centralized control panel which serves as the receiving and distribution point for electrical power and for control signals for the entire conveyor system. Typically, the control panel is supplied by utility company power lines with 3-phase, 480 volts through a main disconnect switch and power at 480 or 120 volts is applied through control devices in the panel to the conveyor drive motors and actuators of various types in the conveyor system. A programmable controller in the panel provides programmed logic for system control. It responds to a large number of input signals from signal input devices in the conveyor system and produces, according to the user program of the controller, a large number of signals for controlling various output devices. Input devices, such as switching contacts and photo sensors, mostly are two state devices and the output devices include motors, electrically actuated pneumatic valves, positioning solenoids and electrically energized clutches and lamps most of which are two state devices.
In the fabrication of conveyor systems of the type described above, it is the usual practice of the conveyor manufacturer to construct the control panel in its own facility for subsequent installation at the factory in which the conveyor is to be used. Likewise, the conveyor structure is built in sections or sub-sections in the conveyor manufacturers plant and then put together in the factory. The control panel generally comprises a floor mounted cabinet with a rear wall, called the back panel, on which the electrical components of the system are mounted. Because of the large number and size of the components, the cabinet and back panel may be seven feet in height and twenty or more feet in length and, occupies a significant amount of factory floor space. In construction, the back panel, usually made up of several joined sections, is laid out as a horizontal work table and the components are mounted thereon in specified locations with wiring troughs or channels built onto the panel for running wires between components. The components include power line terminals, a main switch, overvoltage/overcurrent protection devices, motor starters, relays, indicator lamps, and a programmable controller. The panel is also provided with input field wiring terminals and output field wiring terminals. Each input terminal is connected by panel wiring to one of the components on the panel and each of the output terminals is connected by panel wiring to one of the components on the panel. This arrangement permits the internal wiring of the control panel to be completed by the conveyor manufacturer before the control panel is delivered to the factory for installation. The field wiring terminals facilitate the on-site connection to the panel of the input devices and output devices, which are mounted on the conveyor. The field wiring of a conveyor system for a system of moderate size and complexity will require the connection of several hundred separate wires and, because each wire originates at the control panel and extends to a particular point on the conveyor system, the individual wires will range in length up to several thousand feet. The field wiring, because of the large number of wires and the length of wires, contributes significantly to the cost of a conveyor system.
Because of the large number of wires and the length and paths of the wire runs, trouble shooting to find faults in the system after the field wiring is installed is especially difficult and time consuming. The use of diagnostic systems has not been practical in the prior art conveyor control systems, partly because it would be necessary to increase the number of manually applied interconnections by several fold, thus increasing the complexity and cost of installation with likelihood of decreased reliability because of the increase chance of wiring errors.
A general object of this invention is to provide an improved electrical control system for an industrial conveyor system which overcomes certain disadvantages of the prior art.